For example, an electromagnetic-solenoid fuel injector is known as a fuel injector that injects and supplies fuel into each cylinder of an internal combustion engine mounted in a vehicle. In this type of fuel injector, energization timing and energization time of a coil housed in a fuel injector body are controlled so that a needle is moved in a valve-opening direction to control fuel injection timing and fuel injection amount.
A method of driving a fuel injector has been provided, in which a coil-applied voltage is set to a high voltage early in valve opening, and is then switched to a low voltage. Such a technique improves valve-opening responsivity by applying the high voltage, and allows low-power drive of the fuel injector through subsequent switching to the low voltage. The high voltage is switched to the low voltage based on a detection current detected by a current detection circuit. That is, when the detection current is determined to arrive at a predetermined target peak value, the applied voltage is switched.
Since a machine difference variation exists in the fuel injection device, a variation probably occurs in an actual drive current, and the fuel injection amount concernedly varies due to such a variation in drive current. In Patent Literature 1, therefore, the amount of a machine difference variation in actual drive current is beforehand stored in a storage, and a target drive current is corrected based on the amount of the machine difference variation.
However, the machine difference variation is not constant between the fuel injection devices, and probably varies with the lapse of time.
A possible cause of a variation in fuel injection amount includes deviation in detection by a current detection circuit in addition to the variation in actual drive current in the fuel injector. In such a case, when it is designed that the applied voltage is switched from the high voltage to the low voltage based on the detection current detected by the current detection circuit as described above, voltage switching timing is shifted due to an error in the detection current. Specifically, shift of a peak point occurs in an actual current. Hence, shift of input energy to the fuel injector occurs, resulting in variations in valve-opening response characteristics of the fuel injector. This concernedly leads to excess and deficiency of the fuel injection amount.